Piezoelectric Accelerometer

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Piezoelectric Accelerometer
ECE 5320 MECHATRONICSSensor Tutorial

• Prepared by Jaime Fernandez
• Department of Electrical and Computer Engineering
  
• Utah State University

Robert H. Bishop, Mechatronics Handbook, figure
19.3
2
Outline

• Reference List
• History
• Piezoelectric Notions
• Acceleration Sensing Notions
• Major Applications
• Basics Principles
• Piezoelectric Accelerometer Design
• Major specifications

3
Reference List

• Robert H. Bishop, Mechatronics Handbook, 2002,
  CRC Press LLC
• Wikipedia, http//en.wikipedia.org/wiki/Piezoel
  ectricity
• Alexander D. Khazan, Transducers and Their
  Elements, Prentice Hall PTR
• Robert H. Bishop, Mechatronics Handbook,
  section 19.2
• Curtis D. Johnson, Process Control
  Instrumentation Technology, Prentice Hall PTR,
  National Instruments.

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History

• A related property known as pyroelectricity, the
  ability of certain mineral crystals to generate
  electrical charge when heated, was known of as
  early as the 19th century, and was named by David
  Brewster in 1824. In 1880, the brothers Pierre
  Curie and Jacques Curie predicted and
  demonstrated piezoelectricity using tinfoil,
  glue, wire, magnets, and a jeweler's saw.
• They showed that crystals of tourmaline, quartz,
  topaz, cane sugar, and Rochelle salt (sodium
  potassium tartrate tetrahydrate) generate
  electrical polarization from mechanical stress.

Wikipedia, http//en.wikipedia.org/wiki/Piezoe
lectricity
5

• Quartz and Rochelle salt exhibited the most
  piezoelectricity. Converse piezoelectricity was
  mathematically deduced from fundamental
  thermodynamic principles by Lippmann in 1881.
• The Curies immediately confirmed the existence of
  the "converse effect," and went on to obtain
  quantitative proof of the complete reversibility
  of electro-elasto-mechanical deformations in
  piezoelectric crystals. (1)

Wikipedia, http//en.wikipedia.org/wiki/Piezoe
lectricity
6
Piezoelectric Notions

• Piezoelectricity is the ability of certain
  crystals to generate a voltage in response to
  applied mechanical stress. The word is derived
  from the Greek piezein, which means to squeeze or
  press. The piezoelectric effect is reversible in
  that piezoelectric crystals, when subjected to an
  externally applied voltage, can change shape by a
  small amount. The deformation, about 0.1 of the
  original dimension in PZT, is of the order of
  nanometers, but nevertheless finds useful
  applications such as the production and detection
  of sound, generation of high voltages, electronic
  frequency generation, and ultra fine focusing of
  optical assemblies. (1)
• In a piezoelectric transducer, the acceleration
  acts on the seismic mass that develops a force on
  piezoelectric quartz, or ceramic crystal, or on
  several crystals. The force causes charges on the
  crystals proportional to the acceleration. (2)

Wikipedia, http//en.wikipedia.org/wiki/Piezoel
ectricity Alexander D. Khazan, Transducers and
Their Elements, Prentice Hall PTR Robert H.
Bishop, Mechatronics Handbook, section 19.2
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Acceleration Sensing Notions

• Direct measurement this is done by sensing the
  acceleration directly.
• Indirect measurement this is done
  differentiating the velocity. In the real world
  is more common integrating a measurement than
  differentiating it.
• The applicability of these techniques depends on
  the type of motion (rectilinear, angular, or
  curvilinear motion) or equilibrium centered
  vibration. For rectilinear and curvilinear
  motions, the direct measurement accelerometers
  are preferred. However, the angular acceleration
  is usually measured by indirect methods. (3)

Robert H. Bishop, Mechatronics Handbook,
section 19.2 Curtis D. Johnson, Process Control
Instrumentation Technology, Prentice Hall PTR,
National Instruments
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Major Applications

• Piezoelectric accelerometer are good sensing
  device for the application were is needed
• high bandwidth
• low power consumption
• ruggedness

As acceleration acts on the mounting surface of
a flat plate shear sensing configuration, the
piezoelectric ceramic element is put into shear
relative to the attached mass.

Robert Shear, Endevco Kavlico Corporation
Piezoelectric Sensors for OEM Applications,
figure 3
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• Applications
• Machine Monitoring. Bearing and gear mesh wear
  typically have characteristic frequencies in the
  210 kHz range.
• Shock Detection. For applications such as
  shipment monitoring, impact detection, or drop
  testing.
• Vehicle Dynamics. handling parameters such as
  ride smoothness, vehicle performance, cargo
  transport, and asset tracking in vehicle.
• Structural Dynamics detect fatigue, resonance,
  and response to load.

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Basics Principles

• These devices utilize a mass in direct contact
  with the piezoelectric component or crystal as
  shown in When a varying motion is applied to the
  accelerometer, the crystal experiences a varying
  force excitation (F ma), causing a proportional
  electric charge q to be developed across it.
• So, where q is the charge developed and dij is
  the piezoelectric coefficient of the material. As
  this equation shows, the output from the
  piezoelectric material is dependent on its
  mechanical properties, dij.

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• These accelerometers are useful for
  high-frequency applications. The roll-off
  typically starts near 100 Hz. These active
  devices have no DC response. Since piezoelectric
  accelerometers have comparatively low mechanical
  impedances, their effect on the motion of most
  structures is negligible.

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• Mathematically, their transfer function
  approximates a third-order system that can be
  expressed as where Kq is the piezoelectric
  constant related to charge (C cm), t is the time
  constant of the crystal, and s is the Laplace
  variable. It is worth noting that the crystal
  itself does not have a time constant t, but the
  time constant is observed when the accelerometer
  is connected to an electric circuit, for example,
  an RC circuit.

Robert H. Bishop, Mechatronics Handbook,
Robert H. Bishop, Mechatronics Handbook, fig
19.22
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• The low-frequency response is limited by the
  piezoelectric characteristic ts / (ts 1), while
  the high frequency response is related to
  mechanical response. The damping factor ? is very
  small, usually less than 0.01 or near zero.
  Accurate low-frequency response requires large t,
  which is usually achieved by use of
  high-impedance voltage amplifiers. At very low
  frequencies thermal effects can have severe
  influences on the operation characteristics.

Robert H. Bishop, Mechatronics Handbook,
14
Piezoelectric Accelerometer Design
Manfred Weber, http//www.mmf.de/
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Manfred Weber, http//www.mmf.de/
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Major specifications
Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
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Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
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Endevco Piezoelectric accelerometer, model
22, lthttp//www.bksv.com/pdf/22.pdfgt
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Advantages of piezoelectric accelerometer
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Suppliers Information

• http//www.columbiaresearchlab.com/index.asp/
• http//www.endevco.com/
• http//www.meas-spec.com/myMeas/default/index.asp/
  
• http//www.summitinstruments.com/
• http//www.ferroperm-piezo.com
• http//www.matsysinc.com/
• http//www.piezosolutions.net/
• http//www.sensortech.ca/
• http//www.vfultrasound.com/
• http//www.xinetics.com/home.html/